Hallowe'en is a part of the ancient Celtic festival of Samhain.Samhain, Gaelic for "summer's end", was one of two major festivals of the Celtic year, which had two seasons: the coming of the light, celebrated at Beltane on May 1st, and the coming of the dark, celebrated at Samhain on November 1st.
October 31st was November Eve, the most potent part of the festival of Samhain, which marked the first day of winter, when cattle and sheep were brought to the barn, fattened beasts were slaughtered, crops were gathered, families came together to prepare food, and fuel was collected.
The fires of Samhain were still blazing in Scotland in the 1860s, when a traveler reported seeing thirty fires, each surrounded by rings of dancers, lighting up the hillsides.
The practice continued until the first World War.
Brands lit from the Samhain fires were carried around fields and hedges and the parish was encircled with light, keeping evil winter spirits at bay.
The Mexican Day of the Dead (Dia de los Muertos) is celebrated at around the same time as Hallowe'en and the two festivals have many parallels.
Both grew out of ancient cultural beliefs about death that later intertwined with Christian faith. In both festivals, the world of the living and the world of the dead come together, but on the Day of the Dead, the spirits are welcomed as guests.
As the Day of the Dead has become more familiar to Americans, Mexicans have begun to celebrate Halloween: masks and costumes are sold with sugar skulls and pan de muertos, schools hold costume contests with Day of the Dead altar contests, and some children go trick-or-treating in costume (pedir muertos).
More about Samhain:
http://www.chalicecentre.net/samhain.htm
More about Dia de los Muertos:
http://www.azcentral.com/ent/dead/articles/dead-history.html
